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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Low-dose high-resolution $\mathrm{TOF}$-$\mathrm{PET}$ using ionization-activated multi-state low-$\mathrm{Z}$ detector media

We propose PET scanners using low atomic number media that undergo a persistent local change of state along the paths of the Compton recoil electrons. Measurement of the individual scattering locations and angles, deposited energies, and recoil electron directions allows using the kinematical constraints of the 2-body Compton scattering process to perform a statistical time-ordering of the scatterings, with a high probability of precisely identifying where the gamma first interacted in the detector. In these cases the Line-of-Response is measured with high resolution, determined by the underlying physics processes and not the detector segmentation. There are multiple such media that act through different mechanisms. As an example in which the change of state is quantum-mechanical through a change in molecular configuration, rather than thermodynamic, as in a bubble chamber, we present simulations of a two-state photoswitchable organic dye, a ‘Switchillator’, that is activated to a fluorescent-capable state by the ionization of the recoil electrons. The activated state is persistent, and can be optically excited multiple times to image individual activated molecules. Energy resolution is provided by counting the activated molecules. Location along the LOR is implemented by large-area time-of-flight MCP-PMT photodetectors with single photon time resolution in the tens of ps and sub-mm spatial resolution. Simulations indicate a large reduction of dose.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

GaAs/Ge crystals grown on Si substrates patterned down to the micron scale

Monolithic integration of III-V compounds into high density Si integrated circuits is a key technological challenge for the next generation of optoelectronic devices. In this work, we report on the metal organic vapor phase epitaxy growth of strain-free GaAs crystals on Si substrates patterned down to the micron scale. The differences in thermal expansion coefficient and lattice parameter are adapted by a 2-μm-thick intermediate Ge layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals evolve during growth towards a pyramidal shape, with lateral facets composed of (111) planes and an apex formed by (137) and (001) surfaces. The influence of the anisotropic GaAs growth kinetics on the final morphology is highlighted by means of scanning and transmission electron microscopy measurements. The effect of the Si pattern geometry, substrate orientation, and crystal aspect ratio on the GaAs structural properties was investigated by means of high resolution X-ray diffraction. The thermal strain relaxation process of GaAs crystals with different aspect ratio is discussed within the framework of linear elasticity theory by Finite Element Method simulations based on realistic geometries extracted from cross-sectional scanning electron microscopy images.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Building a Road from Light to Energy

Representing the Center for Solar and Thermal Energy Conversion (CSTEC), this document is one of the entries in the Ten Hundred and One Word Challenge. As part of the challenge, the 46 Energy Frontier Research Centers were invited to represent their science in images, cartoons, photos, words and original paintings, but any descriptions or words could only use the 1000 most commonly used words in the English language, with the addition of one word important to each of the EFRCs and the mission of DOE energy. The mission of the Center for Solar and Thermal Energy Conversion (CSTEC) is to design and to synthesize new materials for high efficiency photovoltaic (PV) and thermoelectric (TE) devices, predicated on new fundamental insights into equilibrium and non-equilibrium processes, including quantum phenomena, that occur in materials over various spatial and temporal scales.

14 SOLAR ENERGY↗
DOE OSTI2019

Cu-Catalyzed Synthesis of CdZnSe–CdZnS Alloy Quantum Dots with Highly Tunable Emission

Fabrication of quantum dots (QDs) with emission covering a wide spectral region has been persistently intriguing because of their potentials in a range of practical applications such as biological labeling and imaging, solar cells, light-emitting diodes, and next-generation displays. We report the synthesis of CdZnSe–CdZnS core–shell alloy QDs through a Cu-catalyzed solid solution alloying strategy starting from CdSe–CdS core–shell QDs. The resulting CdZnSe–CdZnS alloy QDs exhibit emission profiles covering a wide wavelength range of 470–650 nm while maintaining high photoluminescence quantum yields. In addition, high morphological uniformity of the starting CdSe–CdS QDs can be largely retained in the final alloy QDs. We attribute this alloying process to the high mobility nature of Cu cations in Cd-chalcogenide crystals at elevated reaction temperatures, which allows Cu cations to act as transporting agents to transfer a Zn component into the CdSe–CdS QDs while maintaining the particle integrity. We show that this unique alloying strategy is independent of the shape of the starting QDs and can also be applied to the synthesis of CdZnSe–CdZnS nanorods. We anticipate that our study will instigate the synthesis of various high-quality alloy QDs and other alloy nanocrystals beyond what can be achieved currently.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Computational imaging using a mode-mixing cavity at microwave frequencies

We present a 3D computational imaging system based on a mode-mixing cavity at microwave frequencies. The core component of this system is an electrically large rectangular cavity with one corner re-shaped to catalyze mode mixing, often called a Sinai Billiard. The front side of the cavity is perforated with a grid of periodic apertures that sample the cavity modes and project them into the imaging scene. The radiated fields are scattered by the scene and are measured by low gain probe antennas. The complex radiation patterns generated by the cavity thus encode the scene information onto a set of frequency modes. Assuming the first Born approximation for scattering dynamics, the received signal is processed using computational methods to reconstruct a 3D image of the scene with resolution determined by the diffraction limit. The proposed mode-mixing cavity is simple to fabricate, exhibits low losses, and can generate highly diverse measurement modes. The imaging system demonstrated in this letter can find application in security screening and medical diagnostic imaging.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Scintillator high-gain avalanche rushing photoconductor active-matrix flat panel imager: Zero-spatial frequency x-ray imaging properties of the solid-state SHARP sensor structure

Purpose: The authors are investigating the feasibility of a new type of solid-state x-ray imaging sensor with programmable avalanche gain: scintillator high-gain avalanche rushing photoconductor active matrix flat panel imager (SHARP-AMFPI). The purpose of the present work is to investigate the inherent x-ray detection properties of SHARP and demonstrate its wide dynamic range through programmable gain. Methods: A distributed resistive layer (DRL) was developed to maintain stable avalanche gain operation in a solid-state HARP. The signal and noise properties of the HARP-DRL for optical photon detection were investigated as a function of avalanche gain both theoretically and experimentally, and the results were compared with HARP tube (with electron beam readout) used in previous investigations of zero spatial frequency performance of SHARP. For this new investigation, a solid-state SHARP x-ray image sensor was formed by direct optical coupling of the HARP-DRL with a structured cesium iodide (CsI) scintillator. The x-ray sensitivity of this sensor was measured as a function of avalanche gain and the results were compared with the sensitivity of HARP-DRL measured optically. The dynamic range of HARP-DRL with variable avalanche gain was investigated for the entire exposure range encountered in radiography/fluoroscopy (R/F) applications. Results: The signal from HARP-DRL as a function of electric field showed stable avalanche gain, and the noise associated with the avalanche process agrees well with theory and previous measurements from a HARP tube. This result indicates that when coupled with CsI for x-ray detection, the additional noise associated with avalanche gain in HARP-DRL is negligible. The x-ray sensitivity measurements using the SHARP sensor produced identical avalanche gain dependence on electric field as the optical measurements with HARP-DRL. Adjusting the avalanche multiplication gain in HARP-DRL enabled a very wide dynamic range which encompassed all clinically relevant medical x-ray exposures. Conclusions: This work demonstrates that the HARP-DRL sensor enables the practical implementation of a SHARP solid-state x-ray sensor capable of quantum noise limited operation throughout the entire range of clinically relevant x-ray exposures. This is an important step toward the realization of a SHARP-AMFPI x-ray flat-panel imager.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Inversion of coherent surface scattering images via deep learning network

Coherent surface scattering imaging is a powerful tool for imaging a surface/interface of a thin nanostructure deposited on an opaque substrate. A mathematical conversion of an object image from a scattering pattern is essential for coherent surface scattering imaging to visualize structures of specimens. It has been achieved by using phase retrieval algorithms requiring oversampling in scattering patterns and employing alternating projection approaches. It is a computationally challenging and time-consuming process. In this paper, we demonstrate CSSI-NN, which is a deep learning neural network model to predict images of objects from scattering intensities in coherent surface scattering imaging. This model allowing for the instant outcome from scattering patterns would be tremendously beneficial not only for effective experiments but also for data analysis of phase retrieval.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Frontier nonequilibrium materials science enabled by ultrafast electron methods

Most innovation in materials science and engineering resides in our ability to understand and control the intimate relationship between the structure of materials and their properties. Conventionally, the only route to discovering innovative new material properties has been to explore the structural and compositional phase space that is accessible at (or near) thermodynamic equilibrium. The characterization, manipulation and, ultimately, control of material properties far from equilibrium offers almost completely untapped possibilities for uncovering novel states and phases of materials. Investigations of materials far from equilibrium require the development of new techniques, which are capable of following dynamic processes in materials with extreme spatiotemporal resolution. Thus, ultrafast electron-based methods have become a major new frontier in materials science due to the capability of following dynamics on time scales as short as femtoseconds with the high spatial resolution and sensitivity afforded by electrons. The articles in this issue provide an exciting cross section of the novel research directions that have been enabled at this frontier. Imaging on ultrafast time scales carries critical information on phase transitions, fundamental processes involved in light-harvesting, magnetic, and plasmonic dynamics, the coupling of electronic and nuclear degrees of freedom in materials and has revealed previously hidden, nonequilibrium metastable states of matter that have no equilibrium analog.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Large-area SnO{sub 2}: F thin films by offline APCVD

Highlights: {yields} Large-area (1245 mm x 635 mm) FTO thin films were successfully deposited by offline APCVD process. {yields} The as-prepared FTO thin films with sheet resistance 8-11 {Omega}/{open_square} and direct transmittance more than 83% exhibited better than that of the online ones. {yields} The maximum quantum efficiency of the solar cells based on offline FTO substrate was 0.750 at wavelength 540 nm. {yields} The power of the solar modules using the offline FTO as glass substrates was 51.639 W, higher than that of the modules based on the online ones. -- Abstract: In this paper, we reported the successful preparation of fluorine-doped tin oxide (FTO) thin films on large-area glass substrates (1245 mm x 635 mm x 3 mm) by self-designed offline atmospheric pressure chemical vapor deposition (APCVD) process. The FTO thin films were achieved through a combinatorial chemistry approach using tin tetrachloride, water and oxygen as precursors and Freon (F-152, C2H4F2) as dopant. The deposited films were characterized for crystallinity, morphology (roughness) and sheet resistance to aid optimization of materials suitable for solar cells. We got the FTO thin films with sheet resistance 8-11 {Omega}/{open_square} and direct transmittance more than 83%. X-ray diffraction (XRD) characterization suggested that the as-prepared FTO films were composed of multicrystal, with the average crystal size 200-300 nm and good crystallinity. Further more, the field emission scanning electron microscope (FESEM) images showed that the films were produced with good surface morphology (haze). Selected samples were used for manufacturing tandem amorphous silicon (a-Si:H) thin film solar cells and modules by plasma enhanced chemical vapor deposition (PECVD). Compared with commercially available FTO thin films coated by online chemical vapor deposition, our FTO coatings show excellent performance resulting in a high quantum efficiency yield for a-Si:H solar cells and ideal open voltage and short circuit current for a-Si:H solar modules.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Wide Dynamic Range, 10 kHz Framing Detector for 4D-STEM

Hybrid pixel array detectors (PADs) have expanded the fidelity, frame rate and dynamic range for diffractive imaging in electron microscopes. With their high detective quantum efficiencies (DQE), the noise performance limited is by counting statistics. Consequently, improving the precision and quality of high-speed images requires increasing the linear dynamic range and the maximum usable beam current. Here we describe a new prototype hybrid PAD, our next-generation electron microscope pixel array detector (NG-EMPAD) that expands both the framing speed and dynamic range of our earlier EMPAD design. Like the EMPAD, electrons are detected directly in a 500 μm thick silicon sensor bonded pixel-by-pixel to a custom signal processing integrated circuit (IC). Each pixel in the IC integrates charge carriers produced by the high-energy incident electrons. Here, in-pixel circuitry uses a combination of techniques to extend the dynamic range, including adaptive gain switching and the quantitative excess charge dumping similar to the EMPAD. In-pixel buffering of signals during readout allows acquiring a new image while reading out the previously collected image, yielding an image collection duty cycle of nearly 100%.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microscopic model for all optical switching in ferromagnets

The microscopic mechanism behind the all optical switching (AOS) in ferromagnets has triggered intense scientific debate. Here, the microscopic three-temperature model is utilized to describe AOS in a perpendicularly magnetized ferromagnetic Co/Pt system. We demonstrate that AOS in such a ferromagnet can be explained with the Inverse Faraday Effect (IFE). The influence of the strength and lifetime of the IFE induced field pulse on the switching process are investigated. We found that because of strong spin-orbit coupling, the minimal lifetime of the IFE needed to obtain switching is of the order of 0.1 ps, which is shorter than previously assumed. Moreover, spatial images of the domain pattern after AOS in Co/Pt, as well as their dependence on applying an opposite magnetic field, are qualitatively reproduced.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Real-time monitoring of graphene patterning with wide-field four-wave mixing microscopy

The single atom thick two-dimensional graphene is a promising material for various applications due to its extraordinary electronic, optical, optoelectronic, and mechanical properties. The demand for developing graphene based applications has entailed a requirement for development of methods for fast imaging techniques for graphene. Here, we demonstrate imaging of graphene with femtosecond wide-field four-wave mixing microscopy. The method provides a sensitive, non-destructive approach for rapid large area characterization of graphene. We show that the method is suitable for online following of a laser patterning process of microscale structures on single-layer graphene.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Photoacoustic tomography based on the Green's function retrieval with ultrasound interferometry for sample partially behind an acoustically scattering layer

Acoustically inhomogeneous mediums with multiple scattering are often the nightmare of photoacoustic tomography. In order to break this limitation, a photoacoustic tomography scheme combining ultrasound interferometry and time reversal is proposed to achieve images in acoustically scattering medium. An ultrasound interferometry is developed to determine the unknown Green's function of strong scattering tissue. Using the determined Greens' function, a time-reversal process is carried out to restore images behind an acoustically inhomogeneous layer from the scattering photoacoustic signals. This method effectively decreases the false contrast, noise, and position deviation of images induced by the multiple scattering. Phantom experiment is carried out to validate the method. Therefore, the proposed method could have potential value in extending the biomedical applications of photoacoustic tomography in acoustically inhomogeneous tissue.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Thermodynamic parameters of helium under shock-wave and quasi-isentropic compressions at pressures up to 4800 GPa and compression ratios up to 900

The thermodynamic parameters of a strongly nonideal helium plasma obtained in experimental devices of hemispherical and spherical geometries are presented. Under shock-wave loading in the hemispherical device, the helium plasma was compressed to a density ρ ≈ 0.76 g cm{sup –3} by a pressure P ≈ 83 GPa at a temperature T ≈ 51000 K. Two-cascade spherical experimental devices of two types were used under quasi-isentropic helium plasma compression. In the devices of the first type at the same initial gas pressure in both cavities of the shells, the helium plasma was compressed approximately by a factor of 200 to a density ρ ≈ 8 g cm{sup –3} by a pressure P ≈ 4800 GPa. In the devices of the second type at a ratio of the initial gas pressures in the cavities of about 9: 1, the thermodynamic parameters of a nonideal helium plasma compressed by a factor of 900 to a density ρ ≈ 5 g cm{sup –3} by a pressure P ≈ 3700 GPa were determined. The compressed-plasma pressure was determined from the results of gasdynamic computations. An X-ray radiograph consisting of three betatrons and a multichannel optoelectronic X-ray imaging system was used to determine the positions of the boundaries of the gaseous-helium-compressing steel shell.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Real-time studies of ferroelectric domain switching: a review

Ferroelectric materials have been utilized in a broad range of electronic, optical, and electromechanical applications and hold the promise for the design of future high-density nonvolatile memories and multifunctional nano-devices. The applications of ferroelectric materials stem from the ability to switch polarized domains by applying an electric field, and therefore a fundamental understanding of the switching dynamics is critical for design of practical devices. In this review, we summarize the progress in the study of the microscopic process of ferroelectric domain switching using recently developed in situ transmission electron microscopy (TEM). We first briefly introduce the instrumentation, experimental procedures, imaging mechanisms, and analytical methods of the state-of-the-art in situ TEM techniques. The application of these techniques to studying a wide range of complex switching phenomena, including domain nucleation, domain wall motion, domain relaxation, domain-defect interaction, and the interplay between different types of domains, is demonstrated. The underlying physics of these dynamic processes are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Methods and algorithms for computer synthesis of holographic elements to obtain a complex impulse response of optical information processing systems based on modern spatial light modulators

The possibilities of designing optical devices for data processing and imaging based on the manipulation of coherent light beams by means of spatial light modulators (SLMs) are investigated. A review of commercially available SLMs is presented and the limitations of their complex modulation characteristics are analysed. The main problem of using present-day SLMs is the lack of the ability to modulate directly all states within a unit circle in the complex plane. In this regard, the characteristics of current methods for the synthesis of holographic elements are described that implement a given complex impulse response of the optical system and are optimal for using SLMs with purely amplitude, purely phase, and hybrid amplitude – phase modulation. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Bragg grating inscription in photosensitive materials by an optical replication process

This paper examines the feasibility of producing multiplexed Bragg gratings for use as diffractive optical elements (DOEs) by coherent optical replication of a surface-relief phase grating into thick-film photosensitive materials. The use of such DOEs in light guide plates (LGPs) for optical imaging systems ensures energy-efficient light input into and output from LGPs and allows one to minimise their weight and size. We present simulation results for the interference structure fabrication process and recording of a series of multiplexed diffraction gratings in photosensitive materials. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Iris recognition via plenoptic imaging

Iris recognition can be accomplished for a wide variety of eye images by using plenoptic imaging. Using plenoptic technology, it is possible to correct focus after image acquisition. One example technology reconstructs images having different focus depths and stitches them together, resulting in a fully focused image, even in an off-angle gaze scenario. Another example technology determines three-dimensional data for an eye and incorporates it into an eye model used for iris recognition processing. Another example technology detects contact lenses. Application of the technologies can result in improved iris recognition under a wide variety of scenarios.

47 OTHER INSTRUMENTATION↗